In rotary piston mechanisms of the Wankel-type having a housing defining a multi-lobe cavity and a multi-cornered rotor eccentrically supported for planetary rotation in the housing cavity, considerable effort has been expended to design a seal grid of optimum sealing effectiveness and thereby completely isolate from each other the working chambers defined between the rotor and housing. One of the sealing problem areas of the seal grid is between the seal blade or strip and the slot or groove in the rotor apex and the aligned groove in a seal pin or intermediate seal disposed to extend axially in the rotor apex. The sealing in this area is particularly difficult since, in apex seal assemblies, the gas load on the seals changes as rotor rotates and the pressure within the working chambers changes as the working chambers expand and contract in volumetric size. With these changes in gas pressure differential across the apex seal blade of conventional apex seal assemblies, the seal blade is forced in contact with one side of the aligned grooves in the rotor apex and seal pin and then the other. Thus, as the blade moves from one groove wall to the other, there is, for this brief moment, no positive sealing taking place, only that of a labyrinth. In addition, in a rotary internal combustion engine of the Wankel-type, at low speed, such as during starting and idle, gas pressures are relatively low and, therefore, differential pressure across the seal blade is ineffective and leakage will occur. To overcome these problems, numerous apex seal assemblies have been disigned such as in exemplified in the following U.S. Pats. Nos.
Froede, 3,120,815 dated Feb. 11, 1964 PA1 Paschke, 3,180,560 dated Apr. 27, 1965 PA1 Pratt, 3,899,272 dated Aug. 12, 1975
The Froede patent apparatus employs a spring biased wedge which coacts with the seal blade to cam the latter into contact with, at least, one side of the apex seal groove or slot. This sealing apparatus is not entirely satisfactory because it does not provide a positive seal between the seal blade and the groove in each of the seal pins.
The patent to Paschke discloses an apex seal assembly in which the seal pin is so formed as to engage the seal blade along a contact line. In one embodiment, the groove in the seal pin is enlarged radially inwardly and in another embodiment the seal pin is a slotted annular seal receivable in an annulus in the rotor apex. In both of these embodiments, the abutment of the ends of the gas seal strips is essential for optimum sealing effectiveness. In a third embodiment, there are provided two slotted annular seals. In these patented devices there is no assurance of the maintenance of the line contact between the seal pin and seal blade under all operating conditions because of the inherent manufacturing tolerances which will permit relative movement between the seal components.
The device of the Pratt patent discloses elongated cylindrical seal pins which are longitudinally and transversely split to form a four-piece element extending the width of the rotor. This construction permits one of the pin elements to pivot under high pressure gas to contact the seal blade. Here again, since the gas is the tilting force, at low engine speed and therefore low gas pressure, there is no assurance that line sealing contact will be maintained. Furthermore, oil and other deposits may clog the passages to the outer surfaces of the pin elements.
It is, therefore, an object of this invention to provide an improved apex seal assembly wherein optimum sealing effectiveness is maintained through all normal operating conditions of the engine.
It is another object of the present invention to provide an improved apex seal assembly which provides positive sealing force regardless of the engine operating condition.
It is a further object of this invention to provide an improved apex seal assembly having optimum sealing effectiveness yet relatively simple and inexpensive to fabricate and assemble into the rotor.